The Vertical Structure and Ultraviolet Spectrum of X-Ray Irradiated Accretion Disks in Active Galactic Nuclei

Abstract

Motivated by recent work indicating that the UV continuum in AGN may be produced by reradiation of energy absorbed from X-rays irradiating an accretion disk, we present a calculation of the vertical structures and ultraviolet spectra of X-ray irradiated accretion disks around massive non-rotating black holes. After finding the radial dependence of vertically-integrated quantities for these disks, we solve the equations of hydrostatic equilibrium, energy balance, and frequency-dependent radiation transfer as functions of altitude. To solve the last set of equations, we use a variable Eddington factor method. We include electron scattering, free-free, and HI, HeI, and HeII bound-free opacities and the corresponding continuum cooling processes. While the overall spectral shape predicted by X-ray irradiation may be compatible with observations, the Lyman edge emission feature it predicts is not. This finding raises questions for many otherwise plausible models in which X-ray irradiation plays a major role.